The present invention is directed generally to a gas return railway car hydraulic cushioning device designed to maintain separation between the pressurized gas and hydraulic oil therein, and to a method of converting a hydraulic cushioning unit, adapted for connection to an external spring operated restoring mechanism, to a self-contained gas return unit.
The cushioned underframe of a railway car generally includes a pair of end-of-car cushioning devices or gears at opposite ends of the car for providing a resilient or hydraulically controlled connection between the center sill and coupler. Each gear includes a hydraulic system consisting of two chambers related by valves and ports. These include the high pressure inner cylinder having a piston reciprocal therein and the low pressure outer housing.
Impact energy from coupling, starting and stopping forces is transmitted from the coupler through the outer housing and hydraulic cylinder system to the center sill of the car. As the cylinder closes on the piston through impact, oil is forced from the cylinder into the outer housing through metering ports appropriately sized and placed. The oil is instantly returned behind the piston so the hydraulic cushioning is continuously provided with the cylinder if movement of the unit is reversed.
When external forces are removed from the unit, the piston should be returned to a neutral position so the unit can effectively cushion the next impact. Restoring forces have conventionally been provided either by the repositioning springs of a separate restoring mechanism or by pressurized gas within the cushioning unit itself. Known gears including either restoring system have certain disadvantages.
Since the repositioning springs of mechanical restoring mechanisms are typically situated below the hydraulic cushioning unit, the restoring force is offset from the center line of the cylinder and thereby induces a canting of the unit's housing within the sill. Such off-center loading causes wear on the piston, shaft and other parts with most parts being particularly worn on one side. The purchase and maintenance of the compression spring restoring mechanism adds to the cost of the hydraulic cushioning unit. Breakage of the return springs or other failure of the restoring mechanism can furthermore disable the railway car for normal operation.
Gas return hydraulic cushioning units eliminate the off center forces and maintenance problems associated with mechanical restoring mechanisms but such units to date are either expensive to manufacture or provide an unpredictable spongy cushioning action. "Freight Saver" gas return gears afford predictable cushioning action by incorporating an extra piston to maintain separation between the hydraulic fluid and pressurized gas. The extra piston and associated structure, however increases the manufacturing cost of that gear. Other gas return gears simply allow foaming action between the hydraulic oil and pressurized gas but these generally produce a spongy unpredictable cushioning action due to the compressability of the oil and gas mixture.
Accordingly, a primary object of the invention is to provide an improved gas return hydraulic cushioning unit.
More specifically, an object of the invention is to provide such a unit wherein separation between the hydraulic oil and pressurized gas is maintained without an additional piston or other moving parts.
Another object is to provide such a unit of simple and economical construction.
Another object is to provide such a unit which eliminates the necessity for a separate mechanical restoring mechanism.
Another object is to provide such a unit wherein restoring forces are centrally directed so as to eliminate canting of the housing and one sided wear on many gear parts.
Another object is to provide a practical method of converting a railway car hydraulic cushioning unit adapted for connection to an external spring operated restoring mechanism to a self-contained gas return unit.
Another object is to provide such a method which requires minimum modification to the hydraulic cushioning unit.
Finally, another object is to provide a gas return railway car hydraulic cushion unit which is simple and rugged in construction, economical to manufacture and efficient in operation.